Wireless communication between mobile nodes has become increasingly popular. There are essentially two techniques used for linking nodes in wireless networks. The first technique uses existing cellular networks, which are essentially systems of repeaters wherein the transmitting or originating node contacts a repeater and the repeater retransmits the signal to allow for reception at the destination node. The obvious drawbacks to the cellular systems include significant infrastructure costs and geographic limitations. Because of the significant infrastructure costs it is not practical to have cellular networks in all areas. Furthermore, in times of emergency, such as earthquake, fire, or power interruption the cellular network can become disabled in the precise location where it is needed most.
The second technique for linking nodes is to form a wireless ad-hoc network among all users within a limited geographical region. The wireless ad-hoc network generally includes a collection of mobile nodes that communicate with each other using radio frequency links. These nodes communicate through shared spectrum and access the medium in a distributed manner. Each user participating in the ad-hoc network should be capable of, and willing to, forward data packets and participate in ascertaining if the packet was delivered from the original source to the final destination. The wireless ad-hoc network has a number of advantages over cellular networks. First, the wireless ad-hoc network is more robust, in that it does not depend on a single node, but rather has a number of redundant, fault tolerant, nodes, each of which can replace or augment its nearest neighbor. Additionally, the ad-hoc network can change position and shape in real time.
Many wireless ad-hoc network systems support both distributed contention-based channel access protocol (a protocol in which each node competes for accessing the channel in order to perform data transmission) and distributed reservation-based channel access protocol (a protocol in which each node reserves the time for accessing the channel in order to perform data transmission). For instance, in the Multi-Band Orthogonal frequency division multiplexing (OFDM) Alliance (MBOA) MAC specification, a prioritized channel access (PCA) is used as the contention-based channel access protocol. In PCA, a node utilizes both request-to-send (RTS) and clear-to-send (CTS) control signals to access the medium. Other than PCA, a distributed time slot reservation MAC scheme referred as distributed reservation protocol (DRP) is used as the reservation-based channel access protocol. With the DRP, the time is initially divided into superframes. The superframe is further divided into a number of time slots. The first few time slots are used as a beacon period, while the rest of the time slots are used as a data period. As a result, in the distributed reservation-based channel access protocol, each node in the network sends out a beacon during the beacon period to announce the slot reservation. The conflict can therefore be avoided.
Since ad-hoc node operates on limited battery power, energy efficiency is one of the critical issues. Transmission power control (TPC) is one of the important ways for saving energy. As used herein, the term “TPC” refers to the control of power for transmitting packets between nodes. In addition, if many nodes are crowd together within a small area, their communication ranges are overlapped with each other. Because of the range overlapping, only a small portion of nodes can communicate at a given time. As a result, network congestion is generated. It is therefore desired to develop a TPC scheme that can reduce the communication range for some of the nodes by clustering the network in order to reduces mutual interference and increase spatial reuse and further to increase the spectrum efficiency and the network throughput.
Although many TPC clustering schemes have been proposed for wireless ad-hoc network, many schemes are mainly focusing on the contention-based channel access protocol, but not on the reservation-based channel access protocol. Therefore, there is a need to develop a TPC clustering scheme that can support both of the channel access protocols, i.e., the contention-based channel access protocol and the reservation-based channel access protocol.